Adaptive control method to manage SOC for energy storage in DC electric railways

Incorporating energy storage systems (ESSs) into electric railways has been shown to be advantageous for energy saving and power quality enhancement. For DC railways, the connection method of the ESS to the track may impose restrictions on charging and discharging the ESS to control the state of charge (SOC). Without management of the SOC, the ESS is shown in this study to reach minimum or maximum limits, reducing its effectiveness due to unavailability. Whilst it is possible to oversize the capacity of ESS, this incurs increased costs and requires more physical space. The main objective of this study is to propose and validate a control algorithm that prevents the ESS from reaching the maximum or minimum SOC limits whilst maintaining the benefits of the system. The main concept of the proposed control method is to dynamically update the voltage and current setpoints of the ESS to manage its SOC. The control algorithm is implemented in the MATLAB software and the simulation results are validated against experimental results, using a track emulator and supercapacitor. The findings demonstrate that, with appropriate dynamic charge/discharge control, the SOC levels can be adequately managed and no external load or source is required.